Insulate under floorboards without pulling them all up?

george [dicegeorge] wibbled on Wednesday 13 January 2010 17:51

It sounds perfectly feasible - I suspect 2 lengths up at 1/4 and 3/4 the room would make it pretty easy. Pour in a measured quantity between each pair of joists and use an improvised rake (eg some sort of crossbar fixed on a bit of oval conduit which is a bit flexible but still allows control) to rake the stuff around until it's spread out.

I think you'll regret the leaf blower! But a hoover in blow mode might be perhaps more subtle for that approach.

You might be better off laying good underlay in the upstairs rooms as you go along. That way you'd get reasonable insulation and sound deadening at the same time. Personally I wouldn't want that blown stuff on top of a lathe & plaster ceiling, which someone may need/want to take down at some time in the future.

Are you sure that the cables feeding your sockets etc are going to be compatible with your chosen insulation material? (PVC and polystyrene for example do not get on well). Secondly, have you considered the de-rating effect on the cables of immersing them in insulation?

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If your rooms are average length (12 /14 feet) you could slide lengths of 'Space Blanket' into the voids. First slide a length of hardboard (shiny side up) into the void to prevent the Space Blanket snagging on the plaster nibs and follow up with the Space Blanket. Slide the Space Blanket along the hardboard, pushing with a long garden cane or dowel. Remove and re-use the hardboard. This is the method used for pushing in long lengths of copper pipe when installing central heating pipes.

Cic.

Are you happy to lift *some* of the floorboards? If you lifted every

Alternatively, if you're going to carpet the rooms, you could just put some good underlay over the floor, or even some of that thin reflective insulation quilt.

Cheers Richard

This is the sort of technique which is obvious once it's mentioned, but so hard to think up from first principles.

Another useful technique for my toolkit.

Thnaks uk-d-i-y.

A good method for inserting insulation, I've used it for fibreglass in the past. I can't share the enthusiasm for the space blanket though, IMHO better to drill a few small holes in the boards and just pour in snake oil directly with as little disruption as possible.

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Maybe you're thinking of something different. This is 'Space Blanket' fibreglass in a safe package:

Cic.

Fine if it doesn't snag on the sides of the joists. You need a snug fit and there are always odd nails and splinters. Given that the first board is always the difficult one, I'd lift all the boards, but a section at a time.

I suspect he was thinking of one of the multi foil products like tri-iso9...

Or become obstructed by noggings or herringbone struts between the joists. There's the wiring issue to consider as well.

Cheers Richard

What I'd love to know, by the way, is how to insulate under a suspended *ground* floor without taking it up. The methods under discussion for a first floor won't work here, as there is no ceiling beneath, but a 12 inch ventilated void. I've seen a few suggestions in the past, but nothing that has struck me as brilliant.

Cheers Richard

As it's a lath and plaster ceiling down there then I guess it#s an old house and the boards don't have tongues. Do you really need insulation or is it the draught through the gaps that are the culprit? For floorboard gaps I have been using this excellent stuff

Robert

I'm contemplating that in the kitchen. What I'm thinking of is pulling through 'spaceblanket' and supporting it on tile lath resting on the sub walls. One problem I forsee is where the joists overlap.

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If so, I can well understand his dislike of the foil type insulation ('Airtec' from Screwfix and others), but the 'Space Blanket' product made by Knauf and sold in B&Q, Focus, Wickes etc. appears to compare quite favourably with other products for insulation value. In terms of installing it's better than ordinary fibreglass rolls because it stays fully wrapped and can be floated into position very easily.

Cic.

Exactly, there is scope for a retrofit 'stiff but bendable' insulating material that could be fed through between the joists from one lifted floorboard to another a few metres away and then pulled up (or sprung) tight against the understide of the floorboards - some kind of 'springy space blanket'.

there's a fortune to be made there by someone...

Robert

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Two points - who in the earth thinks of taking down a L & P ceiling when the sensible thing to do is just screw plasterboard over it, if it needs replacing.

Secondly I did this task some years ago in a top floor flat in Aberdeen where the centre part of the attic space had been floored with t&g flooring, so I have hands on experience of doing what the OP wants. I made a 2 wheeled trolley with a clamp suitable for fibreglass insulation - pushed the trolley through from one side to the other and pulled it and the f/g back. All very easy said but it was a nightmare and I would certainly never do it again - the trolley worked ok, but there were various hazards in the cavities which made the pulling through very time consuming, energy absorbing and dirt encrusting !

Having eliminated the concern about ceiling replacement, I would explore whether blowing something in would work. Certainly electric cables will need to be considered but as lighting circuits are the only likely ones, I reckon that's not a problem.

Rob

I would reconsider the need to insulate under the floorboards /at all/.

We have just replaced our square-edged floorboards with T&G. At the same time, we took the opportunity to stick in 100mm of celotex for additional insulation.

It was very surprising how little difference this made. What made the difference was carefully filling all the gaps round the edge of the floor; most of the heat loss was drafts - seal those off and you will snug.

(I still think it was worth adding the insulation in our situation - but we had the floorboards up anyway.)

Apologies, yes I was mistaking your recommendation for the multifoil type pseudo-insulation that floats to the surface here every now and again.

Plastic wrapped fibreglass does sound ideal for this application as long as there are no obstructions. Before bagged fibreglass I pushed regular fibreglass along between the joist as you describe and found that about

If there are obstructions then blown fibre might be a nice solution but I've not seen it on sale to joe public.